OBJCOPY(1)

💖 OBJCOPY(1) — GNU Development Tools 💖

okay bestie, sit down, hydrate, because we're about to talk about objcopy(1) from the GNU Development Tools manual and it is a lot in the best way. she copies object files. she translates them. she is the moment. 🦋

---

✨ NAME ✨

objcopy — copy and translate object files. that's it, that's her whole job description, and she EATS. 👑

---

🌸 SYNOPSIS 🌸

objcopy [-F bfdname|--target=bfdname]
        [-I bfdname|--input-target=bfdname]
        [-O bfdname|--output-target=bfdname]
        [-B bfdarch|--binary-architecture=bfdarch]
        [-S|--strip-all]
        [-g|--strip-debug]
        [--strip-unneeded]
        [-K symbolname|--keep-symbol=symbolname]
        [--keep-file-symbols]
        [--keep-section-symbols]
        [-N symbolname|--strip-symbol=symbolname]
        [--strip-unneeded-symbol=symbolname]
        [-G symbolname|--keep-global-symbol=symbolname]
        [--localize-hidden]
        [-L symbolname|--localize-symbol=symbolname]
        [--globalize-symbol=symbolname]
        [--globalize-symbols=filename]
        [-W symbolname|--weaken-symbol=symbolname]
        [-w|--wildcard]
        [-x|--discard-all]
        [-X|--discard-locals]
        [-b byte|--byte=byte]
        [-i [breadth]|--interleave[=breadth]]
        [--interleave-width=width]
        [-j sectionpattern|--only-section=sectionpattern]
        [-R sectionpattern|--remove-section=sectionpattern]
        [--keep-section=sectionpattern]
        [--remove-relocations=sectionpattern]
        [--strip-section-headers]
        [-p|--preserve-dates]
        [-D|--enable-deterministic-archives]
        [-U|--disable-deterministic-archives]
        [--debugging]
        [--gap-fill=val]
        [--pad-to=address]
        [--set-start=val]
        [--adjust-start=incr]
        [--change-addresses=incr]
        [--change-section-address sectionpattern{=,+,-}val]
        [--change-section-lma sectionpattern{=,+,-}val]
        [--change-section-vma sectionpattern{=,+,-}val]
        [--change-warnings] [--no-change-warnings]
        [--set-section-flags sectionpattern=flags]
        [--set-section-alignment sectionpattern=align]
        [--add-section sectionname=filename]
        [--dump-section sectionname=filename]
        [--update-section sectionname=filename]
        [--rename-section oldname=newname[,flags]]
        [--long-section-names {enable,disable,keep}]
        [--change-leading-char] [--remove-leading-char]
        [--reverse-bytes=num]
        [--srec-len=ival] [--srec-forceS3]
        [--redefine-sym old=new]
        [--redefine-syms=filename]
        [--weaken]
        [--keep-symbols=filename]
        [--strip-symbols=filename]
        [--strip-unneeded-symbols=filename]
        [--keep-global-symbols=filename]
        [--localize-symbols=filename]
        [--weaken-symbols=filename]
        [--binary-symbol-prefixstring]
        [--add-symbol name=[section:]value[,flags]]
        [--alt-machine-code=index]
        [--prefix-symbols=string]
        [--prefix-sections=string]
        [--prefix-alloc-sections=string]
        [--add-gnu-debuglink=path-to-file]
        [--only-keep-debug]
        [--strip-dwo]
        [--extract-dwo]
        [--extract-symbol]
        [--writable-text]
        [--readonly-text]
        [--pure]
        [--impure]
        [--file-alignment=num]
        [--heap=reserve[,commit]]
        [--image-base=address]
        [--section-alignment=num]
        [--stack=reserve[,commit]]
        [--subsystem=which:major.minor]
        [--compress-debug-sections]
        [--decompress-debug-sections]
        [--elf-stt-common=val]
        [--merge-notes]
        [--no-merge-notes]
        [--verilog-data-width=val]
        [-v|--verbose]
        [-V|--version]
        [--help] [--info]
        infile [outfile]

like. okay. that's the shape of her. long list, no notes, absolutely iconic. 💅

---

💜 DESCRIPTION 💜

so the GNU objcopy utility literally copies the contents of one object file into another. she uses the GNU BFD Library to read and write her object files, which is how she can write the destination file in a different format than the source. every little thing she does is controlled by command-line options.

now, lowkey important: objcopy should be able to copy a fully linked file between any two formats. but copying a relocatable object file between any two formats? that may not work as expected. no cap. 🙈

she does her translation work by making temporary files and then deleting them afterwards, which is very clean of her. and because she uses BFD for all the translation work, she has access to all the formats described in BFD — meaning she can recognize most formats without you having to tell her. main character energy fr fr. ✨

a few things she's known for:

• you can generate S-records with her by using an output target of srec (e.g., use -O srec). 🍓
• you can generate a raw binary file by using an output target of binary (e.g., use -O binary). when she does this, she essentially produces a memory dump of the contents of the input object file. all symbols and relocation information get discarded. the memory dump starts at the load address of the lowest section copied into the output file.
• when you're generating an S-record or a raw binary file, it may be helpful to use -S to remove sections containing debugging information. in some cases -R will be useful to remove sections holding info the binary file doesn't need.

⚠️ okay this one matters, bestie: objcopy is not able to change the endianness of its input files. if the input format has an endianness (some formats don't), she can only copy the inputs into file formats that have the same endianness or that have no endianness (e.g., srec). (however… see the --reverse-bytes option. 👀)

---

🎀 OPTIONS 🎀

the files themselves

• infile / outfile — the input and output files, respectively. if you don't specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile. (destructively. she said what she said. 💀)

formats & targets

• -I bfdname, --input-target=bfdname — treat the source file's object format as bfdname instead of trying to deduce it. stop guessing, tell her directly. 💅
• -O bfdname, --output-target=bfdname — write the output file using the object format bfdname.
• -F bfdname, --target=bfdname — use bfdname as the object format for both the input and the output file. i.e., just transfer data from source to destination with no translation. so chill of her. 🧚
• -B bfdarch, --binary-architecture=bfdarch — useful when you're transforming an architecture-less input file into an object file. in that case the output architecture can be set to bfdarch. this option gets ignored if the input file already has a known bfdarch. you can access this binary data inside a program by referencing the special symbols created by the conversion process. those symbols are called _binary_objfile_start, _binary_objfile_end and _binary_objfile_size. e.g. you can transform a picture file into an object file and then access it in your code using these symbols. so girlypop coded. 🖼️

picking and choosing sections

• -j sectionpattern, --only-section=sectionpattern — copy only the indicated sections from the input file to the output file. this option may be given more than once. note that using this option inappropriately may make the output file unusable. wildcard characters are accepted in sectionpattern.

if the first character of sectionpattern is the exclamation point (!) then matching sections will not be copied, even if an earlier use of --only-section on the same command line would otherwise copy it. for example:

          --only-section=.text.* --only-section=!.text.foo

will copy all sectinos matching '.text.*' but not the section '.text.foo'. (yes, "sectinos". we respect the original spelling in this house. 🫶)

• -R sectionpattern, --remove-section=sectionpattern — remove any section matching sectionpattern from the output file. this option may be given more than once. note that using this option inappropriately may make the output file unusable. wildcard characters are accepted in sectionpattern. using both the -j and -R options together results in undefined behaviour. 💀 don't do it bestie.

if the first character of sectionpattern is the exclamation point (!) then matching sections will not be removed even if an earlier use of --remove-section on the same command line would otherwise remove it. for example:

          --remove-section=.text.* --remove-section=!.text.foo

will remove all sections matching the pattern '.text.*', but will not remove the section '.text.foo'.

• --keep-section=sectionpattern — when removing sections from the output file, keep sections that match sectionpattern.
• --remove-relocations=sectionpattern — remove non-dynamic relocations from the output file for any section matching sectionpattern. this option may be given more than once. note that using this option inappropriately may make the output file unusable, and attempting to remove a dynamic relocation section such as .rela.plt from an executable or shared library with --remove-relocations=.plt will not work. wildcard characters are accepted in sectionpattern. for example:

          --remove-relocations=.text.*

will remove the relocations for all sections matching the pattern '.text.*'.

if the first character of sectionpattern is the exclamation point (!) then matching sections will not have their relocation removed even if an earlier use of --remove-relocations on the same command line would otherwise cause the relocations to be removed. for example:

          --remove-relocations=.text.* --remove-relocations=!.text.foo

will remove all relocations for sections matching the pattern '.text.*', but will not remove relocations for the section '.text.foo'.

• --strip-section-headers — strip section header. this option is specific to ELF files. implies --strip-all and --merge-notes.

stripping it down 💅

• -S, --strip-all — do not copy relocation and symbol information from the source file. also deletes debug sections.
• -g, --strip-debug — do not copy debugging symbols or sections from the source file.
• --strip-unneeded — remove all symbols that are not needed for relocation processing, in addition to the debugging symbols and sections stripped by --strip-debug.

symbol-level surgery ✨

• -K symbolname, --keep-symbol=symbolname — when stripping symbols, keep symbol symbolname even if it would normally be stripped. this option may be given more than once.
• -N symbolname, --strip-symbol=symbolname — do not copy symbol symbolname from the source file. this option may be given more than once.
• --strip-unneeded-symbol=symbolname — do not copy symbol symbolname from the source file unless it is needed by a relocation. this option may be given more than once.

---

okay that's where part one wraps, but do NOT go anywhere, there is so much more of her to go, we're literally just getting started. 🫶

• -G symbolname, --keep-global-symbol=symbolname — bestie, this one is a filter. It keeps only symbolname global and demotes literally everything else to local, so nothing else is visible externally. It's giving "you, specifically, may stay." You can pass this more than once if you want a lil VIP list. ⚠️ heads up though — you cannot use this together with --globalize-symbol or --globalize-symbols. They do NOT get along. 💀
• --localize-hidden — for ELF objects specifically: any symbol with hidden or internal visibility gets marked local. And it stacks, so it applies on top of the symbol-specific localization options like -L. 💅
• -L symbolname, --localize-symbol=symbolname — takes a global or weak symbol named symbolname and turns it into a local symbol, so it's not visible externally anymore. Like, "you're staying home now." Repeated as many times as you want. But note: unique symbols are not converted — they simply don't play that game. 🙅‍♀️
• -W symbolname, --weaken-symbol=symbolname — makes symbolname weak. That's it, that's the whole thing. Pass it as many times as you like. ✨
• --binary-symbol-prefix=string — when you're rocking --input-target=binary, this sets string as the base name for the symbols generated off the input file. Those symbols are:

<string>_start
<string>_end
<string>_size

Normally (with no flag), the binary input handler just cooks up the prefix from a mangled version of the input file name plus the _binary prefix. This option lets you say it out loud yourself instead. 🎀

• --globalize-symbol=symbolname — gives symbolname global scoping so it's visible outside the file it's defined in. Glow-up to main character, honestly. Pass it more than once if you want. ⚠️ but no cap: this cannot be used with -G or --keep-global-symbol. Pick a lane, bestie.
• -w, --wildcard — unlocks regular expressions in the symbolnames used by your other command line options. The operators you get are ?, *, \ and [], and you can drop them anywhere in the symbol name. And plot twist: if the first character of the symbol name is !, it flips the sense of the switch for that symbol. For example:

-w -W !foo -W fo*

would make objcopy weaken everything that starts with "fo" except for the symbol "foo". Obsessed with the drama of that. 😌

• -x, --discard-all — do not copy non-global symbols from the source file. Bye 👋
• -X, --discard-locals — do not copy compiler-generated local symbols. (Those usually start with L or ..) Not me, fr fr.
• -b byte, --byte=byte — if interleaving is on (via --interleave), this sets where the range of bytes to keep starts, at the byteth byte. byte can be anything from 0 to breadth-1, where breadth is whatever you gave to --interleave. 🧚
• *-i [breadth*], --interleave[=breadth]** — only copies a range out of every *breadth* bytes. (Header data is untouched, so don't worry about that.) --bytepicks which byte in the range kicks off the copy, and--interleave-width` picks how wide the range is.

This is the one for making files to program ROM, and it's typically used with an "srec" output target. Note that objcopy will complain if you don't also specify --byte — so don't ghost it. 😭

The default interleave breadth is 4, so with --byte set to 0, objcopy would copy the first byte out of every four bytes from input to output.

• --interleave-width=width — used alongside --interleave, this copies width bytes at a time. --byte sets the start of the range, --interleave sets the extent.

Default value is 1. And the rule: width plus the byte value from --byte must not exceed the interleave breadth from --interleave. Math check, bestie. ✏️

Here's the iconic use case — building images for two 16-bit flashes interleaved in a 32-bit bus, by passing -b 0 -i 4 --interleave-width=2 and -b 2 -i 4 --interleave-width=2 to two objcopy commands. If your input was '12345678', the outputs would be '1256' and '3478' respectively. Slay. 🔥

• -p, --preserve-dates — sets the access and modification dates of the output file to match the input file's. Same energy, same timestamps.

It also copies the date stored in a PE format file's header — unless the SOURCE_DATE_EPOCH environment variable is defined. If it is defined, then that variable gets used as the date stored in the header, interpreted as the number of seconds since the Unix epoch. 📅

• -D, --enable-deterministic-archives — deterministic mode, on. When copying archive members and writing the archive index, it uses zero for UIDs, GIDs, timestamps, and consistent file modes for all files. Very "same every time, no chaos."

If binutils was configured with --enable-deterministic-archives, this mode is on by default, and you can turn it off with -U. 🌈

• -U, --disable-deterministic-archives — do not operate in deterministic mode. It's the exact inverse of -D: when copying archive members and writing the archive index, use their actual UID, GID, timestamp, and file mode values.

This is the default — unless binutils was configured with --enable-deterministic-archives.

• --debugging — converts debugging information, if possible. Not the default, because only certain debugging formats are supported and the conversion process can be time consuming. It's giving "worth it but she's slow." 🐢
• --gap-fill val — fills gaps between sections with val. This applies to the load address (LMA) of the sections, and it's done by increasing the size of the section with the lower address, then filling the extra space with val.
• --pad-to address — pads the output file up to the load address address. Done by increasing the size of the last section, and the extra space gets filled with whatever --gap-fill says (default is zero). 🫶
• --set-start val — sets the start address (also known as the entry address) of the new file to val. Just so you know: not all object file formats support setting the start address. 🙈
• --change-start incr, --adjust-start incr — changes the start address (also known as the entry address) by adding incr to it. Same disclaimer: not all object file formats support setting the start address.
• --change-addresses incr, --adjust-vma incr — changes the VMA and LMA addresses of all sections, plus the start address, by adding incr. Some object file formats don't permit section addresses to be changed arbitrarily. ⚠️ And note: this does not relocate the sections. So if the program expects its sections at a certain address and you shift them somewhere else with this option, the program may just... fail. Not a vibe.
• --change-section-address sectionpattern{=,+,-}val, --adjust-section-vma sectionpattern{=,+,-}val — sets or changes both the VMA address and the LMA address of any section matching sectionpattern. If = is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. (See the comments under --change-addresses above.) If sectionpattern doesn't match any sections in the input file, a warning gets issued — unless you're using --no-change-warnings.
• --change-section-lma sectionpattern{=,+,-}val — sets or changes the LMA address of any section matching sectionpattern. LMA = the address where the section gets loaded into memory at program load time. Normally it's the same as the VMA address (which is the address of the section at program run time), but on some systems — especially ones where a program lives in ROM — the two can differ. If = is used, the section address is set to val; otherwise val is added or subtracted. See the comments under --change-addresses above. No match on sectionpattern → warning, unless --no-change-warnings.
• --change-section-vma sectionpattern{=,+,-}val — sets or changes the VMA address of any section matching sectionpattern. VMA = the address where the section sits once the program has started executing. Normally same as the LMA address (where it gets loaded into memory), but again, on some systems — especially ROM-based ones — they can be different. = sets the section address to val; otherwise val is added or subtracted. See the comments under --change-addresses above. No match → warning, unless --no-change-warnings.

Note — changing the VMA of sections in a fully linked binary can be dangerous, because there may be code that expects the sections to be located at their old address. Proceed with awareness, bestie. 💀

• --change-warnings, --adjust-warnings — if --change-section-address or --change-section-lma or --change-section-vma is used and the section pattern doesn't match anything, issue a warning. This is the default behaviour. 📣
• --no-change-warnings, --no-adjust-warnings — do not issue a warning if --change-section-address or --adjust-section-lma or --adjust-section-vma is used, even when the section pattern matches zero sections. Silence, but make it intentional. 🤫
• --set-section-flags sectionpattern=flags — sets the flags for any sections matching sectionpattern. The flags argument is a comma separated string of flag names, and the recognized ones are alloc, contents, load, noload, readonly, code, data, rom, exclude, share, debug, and large. You can set the contents flag for a section that doesn't have contents, but it's not meaningful to clear the contents flag of a section that does have contents — just remove the section instead. Also, not all flags are meaningful for all object file formats. In particular, the share flag is only meaningful for COFF format files and not for ELF format files. And the ELF x86-64 specific flag large corresponds to SHF_X86_64_LARGE. 🎀
• --set-section-alignment sectionpattern=align — sets the alignment for any sections matching sectionpattern. align specifies the alignment in bytes and must be a power of two, i.e. 1, 2, 4, 8.... Sorry to the chaotic ones, no funky numbers allowed. ✨

Okay so real talk before we get into the next batch of flags: setting a section's alignment does not automatically align its LMA or VMA addresses. If those also need to move, you gotta reach for --change-section-lma and/or --change-section-vma yourself.

Also, tiny warning: messing with VMAs can cause problems in fully linked binaries, because there might be code in there that fully expects the contents of the sections to live at their old address. So like… proceed with intention, bestie. 🫶

• --add-section sectionname=filename — adds a brand new section called sectionname while it's copying the file. ✨ The contents of the new section get taken from the file filename, and the size of the section becomes the size of that file. This one only works on file formats that can support sections with arbitrary names. Note — you may need to use --set-section-flags to set the attributes of the newly created section. 💅
• --dump-section sectionname=filename — takes the contents of the section named sectionname and drops them into the file filename, overwriting literally anything that was sitting there before. 🗑️ This is the inverse of --add-section. It's kinda like --only-section, except it does not create a formatted file — it just dumps the contents as raw binary data, without applying any relocations. And yes, you can specify this option more than once. 🔥
• --update-section sectionname=filename — replaces the existing contents of the section named sectionname with the contents of the file filename. The size of the section gets adjusted to the size of the file. The section flags for sectionname stay unchanged. For ELF format files the section-to-segment mapping stays unchanged too — something that is not possible if you do --remove-section followed by --add-section. 👑 Can be specified more than once.

Note — you can use --rename-section and --update-section together to both update and rename a section from one command line. In that case, pass the original section name to --update-section, and hand the original and new section names to --rename-section. 🎀

• --add-symbol name=[section:]value[,flags] — adds a new symbol named name while copying the file. This option may be specified multiple times. 🌈 If a section is given, the symbol gets associated with and made relative to that section; otherwise it's an ABS symbol. Specifying an undefined section results in a fatal error. There is no check for the value — it will be taken exactly as specified. Symbol flags can be specified, and not all flags will be meaningful for all object file formats. By default the symbol will be global. The special flag before=othersym inserts the new symbol in front of the specified othersym; otherwise the symbol(s) get added at the end of the symbol table in the order they appear. 🦋
• --rename-section oldname=newname[,flags] — renames a section from oldname to newname, optionally changing the section's flags to flags in the process. The advantage over using a linker script to do the rename is that the output stays as an object file and does not become a linked executable. 💖 This option accepts the same set of flags as --set-section-flags.

This one is especially helpful when the input format is binary, since that will always create a section called .data. So like, say you wanted to instead create a section called .rodata holding binary data — you could use this command line to achieve it:

objcopy -I binary -O <output_format> -B <architecture> \
 --rename-section .data=.rodata,alloc,load,readonly,data,contents \
 <input_binary_file> <output_object_file>

• --long-section-names {enable,disable,keep} — controls how long section names are handled when processing "COFF" and "PE-COFF" object formats. The default behaviour, keep, is to preserve long section names if any are present in the input file. 🌸 enable and disable forcibly enable or disable the use of long section names in the output object; when disable is in effect, any long section names in the input object get truncated. The enable option will only emit long section names if any are present in the inputs — that's mostly the same as keep, but it's left undefined whether enable might force the creation of an empty string table in the output file. 🙈
• --change-leading-char — some object file formats use special characters at the start of symbols. The most common one is underscore, which compilers often add before every symbol. This option tells objcopy to change the leading character of every symbol when it converts between object file formats. If the object file formats use the same leading character, this option has no effect. Otherwise it will add a character, or remove a character, or change a character, as appropriate. 💅
• --remove-leading-char — if the first character of a global symbol is a special symbol leading character used by the object file format, remove that character. The most common symbol leading character is underscore, so this will remove a leading underscore from all global symbols. Useful if you want to link together objects of different file formats that have different conventions for symbol names. 👑 This is different from --change-leading-char because it always changes the symbol name when appropriate, regardless of the object file format of the output file.
• --reverse-bytes=num — reverses the bytes in a section with output contents. A section length must be evenly divisible by the value given for the swap to be able to take place. Reversing takes place before the interleaving is performed. 🔄

This is typically used in generating ROM images for problematic target systems. For example, on some target boards, the 32-bit words fetched from 8-bit ROMs get re-assembled in little-endian byte order regardless of the CPU byte order. Depending on the programming model, the endianness of the ROM may need to be modified.

Picture a simple file with a section containing these eight bytes: 12345678.

• Using --reverse-bytes=2 for the above example, the bytes in the output file would be ordered 21436587.
• Using --reverse-bytes=4 for the above example, the bytes in the output file would be ordered 43218765.
• Using --reverse-bytes=2 for the above example, followed by --reverse-bytes=4 on the output file, the bytes in the second output file would be ordered 34127856.

• --srec-len=ival — meaningful only for srec output. Sets the maximum length of the Srecords being produced to ival. 🧚 This length covers both address, data and crc fields.
• --srec-forceS3 — meaningful only for srec output. Avoids generation of S1/S2 records, creating S3-only record format. ✨
• --redefine-sym old=new — changes the name of a symbol old to new. This can be useful when you're trying to link two things together for which you have no source, and there are name collisions. 💀
• --redefine-syms=filename — applies --redefine-sym to each symbol pair "old new" listed in the file filename. filename is simply a flat file, with one symbol pair per line. Line comments may be introduced by the hash character. This option may be given more than once. 🍓
• --weaken — changes all global symbols in the file to be weak. Useful when building an object which will be linked against other objects using the -R option to the linker. 🔗 This option is only effective when using an object file format which supports weak symbols.
• --keep-symbols=filename — applies --keep-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🎀
• --strip-symbols=filename — applies --strip-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🗑️
• --strip-unneeded-symbols=filename — applies --strip-unneeded-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🧹
• --keep-global-symbols=filename — applies --keep-global-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🌟
• --localize-symbols=filename — applies --localize-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🌈
• --globalize-symbols=filename — applies --globalize-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

Note: this option cannot be used in conjunction with the -G or --keep-global-symbol options. 🚫

• --weaken-symbols=filename — applies --weaken-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. 🦋
• --alt-machine-code=index — if the output architecture has alternate machine codes, use the index-th code instead of the default one. Useful in case a machine is assigned an official code and the tool-chain adopts the new code, but other applications still depend on the original code being used. For ELF based architectures, if the index alternative does not exist then the value is treated as an absolute number to be stored in the e_machine field of the ELF header. 👑
• --writable-text — marks the output text as writable. This option isn't meaningful for all object file formats. ✍️
• --readonly-text — makes the output text write protected. This option isn't meaningful for all object file formats. 🔒
• --pure — marks the output file as demand paged. lowkey, this option isn't meaningful for all object file formats. 💅
• --impure — marks the output file as impure. same energy: this option isn't meaningful for all object file formats. 🫶
• --prefix-symbols=string — every symbol in the output file gets string glued to the front. ✨
• --prefix-sections=string — every section name in the output file gets string glued to the front. 🎀
• --prefix-alloc-sections=string — every name of every allocated section in the output file gets string glued to the front. 🦋
• --add-gnu-debuglink=path-to-file — creates a .gnu_debuglink section that contains a reference to path-to-file and adds it to the output file. Note: the file at path-to-file must exist. part of adding the .gnu_debuglink section is embedding a checksum of the contents of the debug info file into the section. 🔥

if the debug info file is built in one location but it's gonna be installed later into a different location, then do not use the path to the installed location. --add-gnu-debuglink will fail because the installed file does not exist yet. instead, put the debug info file in the current directory and use --add-gnu-debuglink without any directory components, like this:

objcopy --add-gnu-debuglink=foo.debug

at debug time, the debugger will attempt to look for the separate debug info file in a set of known locations. the exact set varies depending on the distribution being used, but it typically includes:

• the same directory as the executable.
• a sub-directory of the directory containing the executable called .debug.
• a global debug directory such as /usr/lib/debug.

as long as the debug info file has been installed into one of these locations before the debugger is run, everything should work correctly. 💖

• --keep-section-symbols — when stripping a file, maybe with --strip-debug or --strip-unneeded, keep any symbols that specify section names, which would otherwise get stripped. 👑
• --keep-file-symbols — when stripping a file, maybe with --strip-debug or --strip-unneeded, keep any symbols that specify source file names, which would otherwise get stripped. 🫶
• --only-keep-debug — strips a file by removing contents of any sections that would not be stripped by --strip-debug, and leaves the debugging sections intact. in ELF files, this preserves all note sections in the output. 💀

note — the section headers of the stripped sections are preserved, including their sizes, but the contents of the section are discarded. the section headers are preserved so that other tools can match up the debuginfo file with the real executable, even if that executable has been relocated to a different address space.

the intention is that this option gets used together with --add-gnu-debuglink to create a two part executable. one: a stripped binary that takes up less space in RAM and in a distribution. two: a debugging information file that's only needed if debugging abilities are required. the suggested procedure to create these files is:

1. link the executable as normal. assuming it's called "foo" then...
2. run objcopy --only-keep-debug foo foo.dbg to create a file containing the debugging info.
3. run objcopy --strip-debug foo to create a stripped executable.
4. run objcopy --add-gnu-debuglink=foo.dbg foo to add a link to the debugging info into the stripped executable.

note — the choice of .dbg as an extension for the debug info file is arbitrary. also the --only-keep-debug step is optional. you could instead do this: 1. link the executable as normal. 2. copy foo to foo.full. 3. run objcopy --strip-debug foo. 4. run objcopy --add-gnu-debuglink=foo.full foo. i.e., the file pointed to by --add-gnu-debuglink can be the full executable. it does not have to be a file created by the --only-keep-debug switch.

note — this switch is only intended for use on fully linked files. it does not make sense to use it on object files where the debugging information may be incomplete. besides, the gnu_debuglink feature currently only supports the presence of one filename containing debugging information, not multiple filenames on a one-per-object-file basis.

• --strip-dwo — removes the contents of all DWARF .dwo sections, leaving the remaining debugging sections and all symbols intact. this option is intended for use by the compiler as part of the -gsplit-dwarf option, which splits debug information between the .o file and a separate .dwo file. the compiler generates all debug information in the same file, then uses --extract-dwo to copy the .dwo sections to the .dwo file, then --strip-dwo to remove those sections from the original .o file. 🧚
• --extract-dwo — extracts the contents of all DWARF .dwo sections. see --strip-dwo for more info. 🌸
• --file-alignment num — specifies the file alignment. sections in the file will always begin at file offsets that are multiples of this number. defaults to 512. [this option is specific to PE targets.] 💅
• --heap reserve, --heap reserve,commit — specifies the number of bytes of memory to reserve (and optionally commit) to be used as heap for this program. [this option is specific to PE targets.] 🍓
• --image-base value — uses value as the base address of your program or dll. this is the lowest memory location that will be used when your program or dll is loaded. to reduce the need to relocate and improve performance of your dlls, each should have a unique base address and not overlap any other dlls. the default is 0x400000 for executables, and 0x10000000 for dlls. [this option is specific to PE targets.] 🔥
• --section-alignment num — [this option is specific to PE targets.] 👑

sets the section alignment field in the PE header — if one is present in the binary. sections in memory will always begin at addresses that are a multiple of this number. defaults to 0x1000.

note — if a section's LMA or VMA addresses are no longer aligned, and those addresses have not been set via the --set-section-lma or --set-section-vma options, and the file has been fully relocated, then a warning message will be issued. it's then up to the user to decide if the LMA and VMA need updating.

• --stack reserve, --stack reserve,commit — specifies the number of bytes of memory to reserve (and optionally commit) to be used as stack for this program. [this option is specific to PE targets.] 🫶
• --subsystem which, --subsystem which:major, --subsystem which:major.minor — specifies the subsystem under which your program will execute. the legal values for which are "native", "windows", "console", "posix", "efi-app", "efi-bsd", "efi-rtd", "sal-rtd", and "xbox". you may optionally set the subsystem version also. numeric values are also accepted for which. [this option is specific to PE targets.] 💖
• --extract-symbol — keeps the file's section flags and symbols but removes all section data. specifically, this option:
  • removes the contents of all sections.
  • sets the size of every section to zero.
  • sets the file's start address to zero.

this option is used to build a .sym file for a VxWorks kernel. it can also be a useful way of reducing the size of a --just-symbols linker input file. 🌈

• --compress-debug-sections — compresses DWARF debug sections using zlib with SHF_COMPRESSED from the ELF ABI. note — if compression would actually make a section larger, then it is not compressed. ✨
• --compress-debug-sections=none, --compress-debug-sections=zlib, --compress-debug-sections=zlib-gnu, --compress-debug-sections=zlib-gabi, --compress-debug-sections=zstd — for ELF files, these options control how DWARF debug sections are compressed.
  • --compress-debug-sections=none is equivalent to --decompress-debug-sections.
  • --compress-debug-sections=zlib and --compress-debug-sections=zlib-gabi are equivalent to --compress-debug-sections.
  • --compress-debug-sections=zlib-gnu compresses DWARF debug sections using the obsoleted zlib-gnu format. the debug sections are renamed to begin with .zdebug.
  • --compress-debug-sections=zstd compresses DWARF debug sections using zstd.

note — if compression would actually make a section larger, then it is not compressed nor renamed. 💀

• --decompress-debug-sections — decompresses DWARF debug sections. for a .zdebug section, the original name is restored. 🦋
• --elf-stt-common=yes, --elf-stt-common=no — for ELF files, these options control whether common symbols should be converted to the "STT_COMMON" or "STT_OBJECT" type. --elf-stt-common=yes converts common symbol type to "STT_COMMON". --elf-stt-common=no converts common symbol type to "STT_OBJECT". 🎀
• --merge-notes, --no-merge-notes — for ELF files, attempt (or do not attempt) to reduce the size of any SHT_NOTE type sections by removing duplicate notes. 🌸
• -V, --version — shows the version number of objcopy. ⭐
• --verilog-data-width=bytes — for Verilog output, this option controls the number of bytes converted for each output data element. the input target controls the endianness of the conversion. 🧚
• -v, --verbose — verbose output: lists all object files modified. in the case of archives, objcopy -V lists all members of the archive. 💅
• --help — shows a summary of the options to objcopy. 🫶
• --info — displays a list showing all architectures and object formats available. 👑
• @file — reads command-line options from file. the options read are inserted in place of the original @file option. if file does not exist, or cannot be read, then the option will be treated literally, and not removed. 🔥

options in file are separated by whitespace. a whitespace character may be included in an option by surrounding the entire option in either single or double quotes. any character (including a backslash) may be included by prefixing the character to be included with a backslash. the file may itself contain additional @file options; any such options will be processed recursively. 💖

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💫 SEE ALSO 💫

okay so when you're done copying objects and you're like "what now bestie", here's the squad you go hang with:

• ld(1) — the linker, the one who actually puts it all together 🫶
• objdump(1) — the nosy bestie who reads your object files back to you, obsessed with her honestly
• and the Info entries for binutils — yes ma'am, there's a whole other manual situation going on there, go look 👑

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🎀 COPYRIGHT 🎀

Copyright (c) 1991-2026 Free Software Foundation, Inc.

k so legal moment, but make it cute: you are granted permission to copy, distribute, and/or modify this document, no cap, under the terms of the GNU Free Documentation License, Version 1.3 — or any later version published by the Free Software Foundation, whichever vibe you're on. ✨

the conditions? there are no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. so like, zero of each, we love a clean slate 💅

and a copy of the license itself is included in the section titled "GNU Free Documentation License", so if you wanna read the whole thing it's right there waiting for you 🦋

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okay that's literally the whole page bestie, we made it 🥹 this was binutils-2.47, dated 2026-09-19, and yes that's the OBJCOPY(1) era, iconic, no notes 🌈💖 go copy some object files, you're gonna slay 💅✨